President Donald Trump on Friday ordered U.S. Trade Representative Robert Lighthizer to start the process of imposing new tariffs on all remaining imports from China, worth $300 billion, in Washington's latest push to force more significant concessions from Beijing.

Trump stepped up pressure on China after raising U.S. tariffs on $200 billion worth of Chinese goods to 25 percent from 10 percent earlier Friday, in the biggest escalation yet in Washington's tit-for-tat trade war with Beijing.

"The president...ordered us to begin the process of raising tariffs on essentially all remaining imports from China," Lighthizer said in a statement.

Concerns have grown that the protracted trade war could further roil global markets and cast a shadow over the world economy. China has pledged to retaliate against the U.S. tariff hike, but it is not clear what action Beijing will take.

Trump said the United States will continue trade negotiations with China in an effort to address what he regards as Beijing's unfair trade practices, and that whether or not U.S. tariffs on Chinese goods are removed will depend on how future talks evolve.

The remarks, carried in a Twitter post, suggest two days of negotiations through Friday in Washington have not resulted in a breakdown, despite little progress being made.

Trump said the relationship with Chinese President Xi Jinping remains "a very strong one," and that "conversations into the future will continue."

"In the meantime, the United States has imposed Tariffs on China, which may or may not be removed depending on what happens with respect to future negotiations!" he wrote.

U.S. Treasury Secretary Steven Mnuchin said there are currently no talks with China scheduled in the future. "Nothing planned as of now," he told U.S. business news network CNBC.

Mnuchin and Lighthizer attended the latest round of talks with Chinese Vice Premier Liu He.

Speaking to Chinese state media in Washington, Liu said the two sides agreed to meet as early as possible in Beijing, continue communications and try to advance negotiations.

While they did not set a date to resume talks, a Group of 20 summit slated for late June in Osaka, Japan, will provide a chance for Trump and Xi to meet.

(Robert Lighthizer (R) and Steven Mnuchin)

Lighthizer, Mnuchin and Liu met in a bid to salvage a trade deal that appeared to be within a reach a week ago. Trump accused Beijing of reneging on commitments it had made during months of negotiations.

Liu did not come prepared to offer much more in the way of concessions, Bloomberg news agency said, quoting several people familiar with the talks.

The United States and China had much mutual understanding, but they still had differences over "principle issues," Liu was quoted by Reuters news agency as saying.

China cannot make concessions on those principle issues, he said, but did not provide details.